Stromatolites in Shark Bay, Australia

A scientist examines the stromatolite growths in Shark Bay, Australia. The structures are formed when cyanobacteria and algae growing on the bottom cause the water chemistry to change, and limestone precipitates around the growing organisms. This process continues for hundreds of years or longer, causing rock-like reefs to form.

Shark Bay on the west coast of Australia, the Great Salt Lake (Utah, USA), as well as some freshwater lakes have stromatolites.